ABSORPTION AND TRANSLOCATION OF WATER AND SOLUTES

  The water is absorbed by root hairs of the plant from where it reaches the xylem via cortical cells and passage cell and through the xylem, it reaches the top of the plant where it is transpired by leaves and used for other metabolic activities. Water and minerals are conducted through xylem tissue. While sieving tubes of the phloem vessels are involved in the conduct of sucrose molecules and other assimilates. The upward movement of water from the stem base to treetop is called Ascent of Sap . It may even cover a height of more than 90 metres against the gravitational pull. Because of the fact that the pressure of one atmosphere can normally lift the water column only by about 10 metres, the rise of water up to such heights (90m) needs some special mechanism. Theories of Ascent of Sap Various theories have been proposed to explain the special mechanism (s) involved in the ascent of sap. These theories can be grouped under three categories as given below: 1. Vital Theories a. Wes...

 The plants get two types of environment for water absorption, the external and internal. The external environment includes factors such as a) available soil water, b) concentration of soil solution. c) soil temperature and d) soil aeration. The internal factors include, i) transpiration, ii). absorbing root system and iii) metabolism. I. External Environmental Factors a. Available Soil Water A sufficient amount of water should be present in the soil in such a form, which can readily and easily be absorbed by the plants. Usually, the plants absorb capillary water. Other forms of water in the soil (hygroscopic, gravitational etc.) are not easily available to plants. b. Concentration of Soil Solution The increased concentration of soil solution (due to the presence of more salts in the soil) results in a higher OP. If the OP of soil solution becomes higher than the OP of cell sap in root cells, the water absorption will be greatly suppressed. Therefore, the absorption of water is poo...